Demand for increasing efficiency in photovoltaic devices, such as solar cells is leading to investigation of strategies to obtain more electrical energy from known types of solar cells, such as amorphous silicon and cadmium-telluride (Cd—Te) devices. One area in which improvements may be beneficial is at the interface of the transparent conductive oxide (TCO) layer, and the so-called active layer, eg. amorphous silicon or Cd—Te. As the most commonly used TCO for solar cells is doped tin oxide, there are a number of reasons why the addition of a chemically stable, electrically conductive layer between the TCO and the active layer e.g. titanium oxide, may increase the conversion efficiency of a solar cell so constructed.
Enhancement of various properties of TiO2 thin films has also been reported in the patent literature, for example:
U.S. Pat. No. 4,011,149 describes thin semiconducting electrodes of either single crystal, polycrystalline or amorphous materials. Preferred n-type anodic materials are said to include “suitably doped TiO2”.
U.S. Pat. No. 4,090,933 is a continuation-in-part of U.S. Pat. No. 4,011,149.
U.S. Pat. No. 4,524,091 describes a method of fabricating TiO2 thick film photoanodes by screen printing multiple layers on a substrate, including two TiO2 layers. The resulting structure is then treated to purportedly reduce the electrical resistivity of the printed films.
U.S. Pat. No. 5,028,568 describes an electrically conductive metal oxide particulate membrane having increased electrical conductivity due to utilization of a dopant in a sol-gel process, for example a niobium doped TiO2 ceramic membrane.
U.S. Pat. No. 5,350,644 describes a photovoltaic cell comprising a light transmitting electrically conductive layer deposited on a glass plate or a transparent polymer sheet on which a series of TiO2 layers have been applied. One or more of such TiO2 layers may be doped with a divalent or trivalent metal ion.
U.S. Pat. No. 6,524,647 discloses application of a niobium doped tin oxide coating onto a glass substrate to produce a low-emissivity glass. The coating can optionally be doped with both niobium and other dopants, such as fluorine.
U.S. Pat. No. 6,524,750 describes a method for making a doped TiO2 compound and the compound made thereby. The process, basically, involves mixing TiO2 with an oxide of M (an element having an octagonal coordination structure), heating the mixture for a time and at a temperature sufficient to cause reaction of the TiO2 and oxide of M to form a doped TiO2 and subjecting the doped TiO2 to a reducing atmosphere.
U.S. Pat. No. 6,720,202 describes a photovoltaic cell which includes a semiconductor layer of TiO2 powders, consisting of porous particles of a particular size range and possessing a relatively high bulk density combined with high surface area.
U.S. Pat. No. 6,818,347 describes an alkaline battery cell including an electrolyte provided with an n-type metal oxide additive which improves electrochemical performance. The n-type metal oxide additive is either a doped metal oxide or a reduced metal oxide.
U.S. Pat. No. 7,037,589 describes niobium-titanium films, film stacks including one or more such niobium-titanium films and substrates bearing such films.
U.S. Pat. No. 7,169,733 describes a photocatalyst having first and second semiconductors wherein the first semiconductor may be, for example, nitrogen-doped or carbon-doped TiO2, and the second semiconductor may be metal-doped TiO2 each having increased oxidation or reduction potential upon irradiation by visible light.
WO2007/027498 discloses a multi-layer film stack including a light transmittance optimizing interlayer having a refractive index between 2.3 and 3.5, which may be TiO2 and other suitable substoichiometric metal oxides.
EP 1796 107 describes a transparent conductor to be used in, for example, LCDs, solar cells, and electroluminescent electrodes. The transparent conductor includes a metal oxide of the form M:TiO2 having an anatase-type crystal structure. The electrical conductivity of the transparent conductor is said to be increased while maintaining its transparency by replacing Ti atoms with another metal atom such as Nb, Ta, Mo, As, Sb, W or the like.